If you want to get up to real mischief on a mac and you have a high voltage serial programmer to remove the bootloader delay: when the digispark gets power, hold down meta+s for 5 seconds, then wait ten seconds, and you\'re logged in to a root unix terminal. Next type \"/sbin/mount -uw /\" without quotes, enter, and wait half a second - now the filesystem is writable and you can do whatever you like! It\'ll fully automatically do whatever you want to their computer next time they reboot it - leave their computer turned off and it\'ll run as soon as they try to use it!
Typing meta+s rapidly during start up isn\'t good enough - it needs to be held down, so DigiKeyboard would probably need to be modified to have that functionality?
I think digistump is going to make a high voltage programmer shield later, so this may become plausible with digispark. If you were willing to sacrifice a digispark, you could use my \'upgrade\' program to remove the bootloader, but you\'d need a fuse resetter to fix it back up afterwards, as well as a spare digispark, arduino, or avr programmer to use to reload the bootloader and disable the reset pin again if you wanted to recover the digispark, so that\'s a bit involved at the moment.
On the new solid state drive macs, all this stuff happens extremely quickly so you could be in and out before they\'ve even gotten over the shock of their screen going black and white and text zooming past at an unreadable pace. You could also type in some escape characters to reconfigure the terminal in to raw mode without echo, so they wouldn\'t be able to see the commands the digispark types in, only the results of those commands, meaning you could use \'echo\' to make it say all sorts of crazy things, or use the \'say\' command to use the computer voice to read out text.